In a typical cellular radio system, wireless terminals (also referred to as user equipment unit nodes, UEs, and/or mobile stations) communicate via a radio access network (RAN) with one or more core networks. The RAN covers a geographical area which is divided into cell areas, with each cell area being served by a radio base station (also referred to as a RAN node, a “NodeB”, and/or enhanced NodeB “eNodeB”). A cell area is a geographical area where radio coverage is provided by the base station equipment at a base station site. The base stations communicate through radio communication channels with UEs within range of the base stations.
Moreover, a cell area for a base station may be divided input a plurality of sectors surrounding the base station. For example, a base station may service three 120 degree sectors surrounding the base station, and the base station may provide a respective directional transceiver and sector antenna array for each sector. Stated in other words, a base station may include three directional sector antenna arrays servicing respective 120 degree base station sectors surrounding the base station.
Multi-antenna techniques can significantly increase capacity, data rates, and/or reliability of a wireless communication system as discussed, for example, by Telatar in “Capacity Of Multi-Antenna Gaussian Channels” (European Transactions On Telecommunications, Vol. 10, pp. 585-595, Nov. 1999). Performance may be improved if both the transmitter and the receiver for a base station sector are equipped with multiple antennas (e.g., an sector antenna array) to provide a multiple-input multiple-output (MIMO) communication channel(s) for the base station sector. Such systems and/or related techniques are commonly referred to as MIMO. The LTE standard is currently evolving with enhanced MIMO support and MIMO antenna deployments. A spatial multiplexing mode is provided for relatively high data rates in more favorable channel conditions, and a transmit diversity mode is provided for relatively high reliability (at lower data rates) in less favorable channel conditions.
In a downlink from a base station transmitting from a sector antenna array over a MIMO channel to a wireless terminal in the sector, for example, spatial multiplexing (or SM) may allow the simultaneous transmission of multiple symbol streams over the same frequency from the base station sector antenna array for the sector. Stated in other words, multiple symbol streams may be transmitted from the base station sector antenna array for the sector to the wireless terminal over the same downlink time/frequency resource element (TFRE) to provide an increased data rate. In a downlink from the same base station sector transmitting from the same sector antenna array to the same wireless terminal, transmit diversity (e.g., using space-time codes) may allow the simultaneous transmission of the same symbol stream over the same frequency from different antennas of the base station sector antenna array. Stated in other words, the same symbol stream may be transmitted from different antennas of the base station sector antenna array to the wireless terminal over the same time/frequency resource element (TFRE) to provide increased reliability of reception at the wireless terminal due to transmit diversity gain. As used herein, the term time-frequency-resource-element (TFRE) may refer to a time-frequency-code-resource-element.
To further increase throughput at a sector/cell edge (also referred to as a soft handover or border area) using High Speed Downlink Packet Access (HSDPA), Multi-Point-HSDPA (MP-HSDPA, also referred to as multi-flow-HSDPA or MF-HSDPA) has been proposed for 3rd Generation Partnership Project (3GPP) communications. In MP-HSDPA, transport blocks of a data stream may be transmitted from two different sectors/cells of the same or different base stations to a same wireless terminal in a border area between the sectors/cells. Intra Node-B aggregation (also referred to as intra node Multi-Point communications) occurs when different transport blocks of a data stream are transmitted from two different sectors of a same base station to a wireless terminal, and Inter Node-B aggregation (also referred to as inter node Multi-Point communications) occurs when different transport blocks of a data stream are transmitted from sectors of different base stations to a wireless terminal. MP-HSDPA may thus provide advantages of parallel data streams like MIMO where the spatially separated antennas are taken from different sectors/cells.
When MP-HSDPA is configured for transmission (from two cells/sectors of a same base station or from two cells/sectors of different base stations) to a MIMO capable wireless terminal with only two receive antennas, however, a maximum multiplex gain may be two (determined as the lesser of the number of transmitter antennas or receiver antennas used for the wireless link). Scheduling two streams with Multi-Point operation from the same sector/cell during Multi-Point communications from different sectors/cells may thus result in a loss in wireless terminal and/or sector throughput. Use of MP-HSDPA with two MIMO streams from the same sector/cell may not provide useful gains in throughput, and in fact, use of MP-HSDPA with two MIMO streams from the same sector/cell may result in a loss in sector throughput.